A key challenge in biology and medicine is to understand how network of interacting genes gives rise to cellular behavior. Experimental limitations and the big data generated by 'omics technologies requires the development of quantitative approaches to overcome this challenge. In the context of mathematical models this challenge takes form of predicting complex dynamic behavior of gene and signaling networks inside cells. Construction of appropriate models is difficult due to large uncertainty in the state of the cell, the efficiency of its enzymes, and the form of interactions between genes.